The fact is that, besides its unpleasing form, especially when the major axis is vertical, the use of the ellipse entails such an annoying series of difficulties as greatly to increase the trouble and consequent cost of execution. The constant change of curvature, the troublesome methods of striking it, and of finding the true lines of the arch-joints, not to mention the mathematical fact that the same joint line is never true both for the extrados and intrados, and that, if the rib-mould remains unchanged in depth, the extrados and intrados cannot be both true ellipses at all; all these furnish quite sufficient practical reasons for its rejection in cases where not only is there no necessity but an abstract mathematical idea to be satisfied by its use, but the beauty of the work is greatly improved by dispensing with it.
Though the pointed arch was introduced from purely constructive reasons, there was another of a more æsthetical nature, which rendered its adoption more general when once introduced. It was a double one; not only did the general tendency towards lofty proportions render it necessary to make use of an arch more in harmony with the general feeling of the architecture, but the rejection of a fixed code of proportions for pillars and other parts demanded for the arch an equal power of varying its own proportions. The semicircular arch is absolute and invariable, and though the use of smaller segments would meet the case in one direction, there were no means of proportioning it to features of increasing height. This was attempted both in Romanesque and Byzantine works by the expedient of stilting, but this is, after all, more a semblance than a reality. As in cases already cited, the mathematical solution of the problem is the ellipse; but only imagine anything so unpleasing as a series of elliptical arches placed the length-way upwards! Good taste would not suffer it. But the pointed arch at once met the difficulty. To illustrate my meaning, I will beg you to take an internal bay of a Norman cathedral ([Fig. 146]), and to suppose yourselves to have to increase its height throughout in the ratio of one-third ([Fig. 147]).
| Fig. 146. | Fig. 147. |
You first, after setting out your widths as in the original, increase the whole height and that of each storey by one-third; you then increase the pillars and the jambs of the triforium and clerestory windows in the same proportion: this brings you to a stand, for the arches, being semicircles, are invariable. Either you must leave them unaltered and throw all the extra height into the wall above them, or you must stilt them each to the extent of one-third of their height unless you can make use of an elastic arch which will change its proportion at pleasure. The ellipse occurs and meets the case, but it offends your eye. At length, however, the pointed arch suggests itself, and gets rid of the whole difficulty. So similar are a Romanesque and an Early Pointed bay in all other respects, that the change of proportion which I have described seems at once to effect the whole change in style.
Had the constructional motive alone existed, the pointed form would have been confined to arches of considerable span; but the demand for a variable arch adding æsthetic to the constructional claim, caused its speedy adoption in positions where strength alone would not have demanded it, though the semicircle, the plain segment, and the segmental pointed arch, were, at all subsequent periods of the style, used side by side with the true pointed form.
I have been the more particular in showing the true reasons for the change in the form of the arch, because the great majority of writers treat it purely as a matter of taste and of altered fashion; indeed, some excellent writers on the history of Mediæval architecture have strangely imagined that the pointed arch had a greater outward thrust than the round, and that the increased projection of the buttresses was necessitated by its use, instead of the two being simultaneously introduced as a double means of avoiding the evils experienced from the great thrust of the round arch and the small buttresses by which it had, during the Romanesque period, been accompanied.
I will now close my present lecture, but hope in the next to carry on the same inquiry into a number of other details, as well as into the general spirit and principles of the architecture of which I am treating, and to add some practical remarks on the application of the rationale thus traced out to our present revival of the style, and such developments as it may give rise to.